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A167768 First of 4 or more consecutive integers with equal values of phi(phi(n)). 2
1, 7, 31, 32, 2694, 131071, 50802031105 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
Next term > 1266046940 (last term of A167767 b-file). - Michel Marcus, Jun 23 2013
No other terms < 1.32*10^12. - Jud McCranie, Jul 19 2017
LINKS
EXAMPLE
p2(1) = p2(2) = p2(3) = p2(4) = 1, p2(7) = p2(8) = p2(9) = p2(10) = 2.
MATHEMATICA
a[n_] := EulerPhi[EulerPhi[n]]; Select[Range[10000], a[#] == a[# + 1] && a[# + 1] == a[# + 2] && a[# + 2] == a[# + 3] &] (* G. C. Greubel, Jun 23 2016 *)
PROG
(PARI) pp(n) = eulerphi(eulerphi(n))
isA167768(n) = pp(n)==pp(n+1) && pp(n+1)==pp(n+2) && pp(n+2)==pp(n+3) \\ Michael B. Porter, Nov 24 2009
CROSSREFS
Cf. A167767 (of which this list is a subset), A167766.
Sequence in context: A065916 A122654 A184121 * A103630 A205711 A040064
KEYWORD
more,nonn,hard
AUTHOR
Fred Schneider, Nov 11 2009
EXTENSIONS
Edited by N. J. A. Sloane, Nov 12 2009
a(7) added by Jud McCranie, Jul 17 2017
STATUS
approved

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Last modified February 22 21:30 EST 2024. Contains 370265 sequences. (Running on oeis4.)